This invention relates to an apparatus for spinal column fixation. More particularly, but not by way of limitation, this invention relates to a mechanical device used to obtain a rigid posterior spinal column fixation in order to obtain a rigid posterior spinal column bony fusion for disabling back and leg pain.
In one embodiment, the apparatus includes a posterior fixation device which is attached to the involved vertebral bodies. The attachment is made by pedicle screws penetrating into the vertebral body with rigid attachment to ball-and-socket clamps and rods.
The invention also may include a pair of intervertebral metallic or radiolucent wedges inserted into the disc space of the involved vertebrae to increase the stability of the spinal column anteriorly and to avoid breakage of the pedicle screw. Additionally, the application also discloses a method of placing the fixation and wedge device in a posterior lateral approach.
Posterior spinal fusions have been performed on millions of people since at least the early 1900's. The principle of bony fusion has been and still is stabilization or prevention of motion between two adjacent vertebral bodies.
The most recent attempt to stop motion of the spinal column in order to obtain spinal fusion is internal fixation. One design consist of a series of hooks, rods, screws and wires attached to the lamina or spinous processes to correct deformity or to stabilize the spine.
Another design utilizes screws inserted posteriorly through the pedicle into the vertebral body connecting to plates, rods and clamps to stabilize the two adjacent segments.
The prior art pedicle screw devices have different functions. One function includes the correction of the degenerative curve of the lumbar spine between L3 and S1 or traumatic deformities. These devices have the internal purpose of this device is correction of a deformity through two vertebra such as seen in U.S. Pat. No. 4,987,892 to Martin H. Krag, and in U.S. Pat. No. 5,047,029 to Max Aebi and Robert Mathys, Jr.
Another function includes rigidly fixing the spinal column using a combination of intra-vertebral screws, plates, rods and clamps. In general, see U.S. Pat. Nos. 4,615,681, 4,648388, 4,655,199 to Steffie; 4,754,326, to Burton; 4,950,269 to Gaines; 4,653,481 to Howland; 4,913,134 to Luque; 4,836,196 to Parke and Weinstein; 4,946,458 to Harms; 5,030,220 to Howland; 4,887,595 to Heinig; and 5,042,982 to Harms.
Another function includes flexible or semi-rigid fixation shown in U.S. Pat. Nos. 4,913,134 to Luque; and, 4,743,260 to Buttem.
The present invention utilizes the rigid posterior fixation device which is attached to the involved vertebral bodies through pedicle screws connected with a series of operably associated ball-and-socket clamps and rods. One such device using a ball connector is seen in U.S. Pat. No. 4,946,458 to Harms. However, the prior art devices include several disadvantages. For instance, many devices were susceptible to breakage, and once breakage occurs, the devices are very difficult to retrieve. Also, the mechanism of clamps and rods is very complicated and difficult for the surgeon to install.
Furthermore, in both the rigid and flexible type of devices, the pedicle screw developed excessive motion and toggle. This in turn would cause the plate to become loose thereby allowing the plate to slide back and forth causing irritation, lack of fixation, and thus failure of fusion.
The rigid devices without inter-body fusion or rigid spacer will result in breakage in the screw because of mechanical factors. The greatest portion of the weight of the individual is taken through the vertebral body and disc. The center of motion of the vertebral segments is located in the posterior aspect of the disc. In the lower lumbar spine the greatest amount of motion is flexion and extension of the trunk, therefore, the intervertebral segment motion is mainly to the anterior frontal or posterior backward movement. Rigid posterior fixation is at a mechanical disadvantage because the forces of weight and motion are anterior to the rigid posterior fixation device. With repetitive motion the device either breaks or becomes loosened. With loosening or breakage, the motion will increase leading to more pain and failure.
Sciatica is pain which shoots down the posterior lateral aspect of the leg. Sciatica is caused by impingement or encroachment on the neural elements in the lumbar spine. Recent studies indicate that intervertebral body fusion is the most effective relief of sciatica. This is because the intervertebral disc is the mechanical center of motion between the intervertebral bodies, and the majority of the body weight of the individual is taken through the vertebral bodies.
Prior art devices are designed and placed in the intervertebral disc comprise several concepts. One is to replace the disc which has been removed with an artificial disc material which can function and behave biomechanically similar to the normal intervertebral disc when inserted in the space.
A second includes maintaining the disc height with no attempt at inter-body fusion. A spacer is placed in after removal of the intervertebral disc.
A third involves maintaining height and obtaining a fusion with a fenestrated spacer that will contain a bone graft. The fenestrated spacer is placed in directly posteriorly under the neural elements.
This invention solves these problem by combining the wedge insert anteriorly and the rigid posterior fixation device allowing the patient to obtain a solid, rigid fixation. The purpose of the wedge is to obtain anterior stabilization, restoration of intervertebral disc height, normal physiological lumbar lordosis, and intervertebral body bony fusion in the human spinal column. The posterior device stabilizes the mechanical dynamics associated with posterior forces, and the wedge compensates the forces associated with the anterior forces.